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Erik Nijeboer / Bram Bruekers Oktober 2017 Power Delivery Network Analysis
Erik Nijeboer / Bram Bruekers
Oktober 2017
Power Delivery Network Analysis
2 © 2017 Cadence Design Systems, Inc.
• Why Power Delivery Network Analysis?
• Analysis types, – DC simulation
– Thermal aware simulation
– AC simulation
• PDN analysis at Prodrive Technologies
• Tools and integration
Agenda
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• DC voltage is the most fundamental criterion for the operation of the circuitry in the system– The voltage supply is allowed to deviate by an amount specified by
the vendor
– This deviation (or fluctuation) of the supply is composed of DC loss and AC noise
– The total voltage tolerance is commonly 5% (or less) of the nominal operating voltage
– If the tolerance is constant, then a reduction in DC loss yields a larger AC noise budget
Why Is Power Distribution Analysis ?
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• Numerous factors have combined to exacerbate the problem– Core voltage levels continue to drop: 1.2V and less are now
common. Total margin drops from 250mv to 60mv
– As voltage is reduced, current requirements typically increase: IR drop = I * R
– Miniaturization of electronics results in fewer layers and higher densities thus reducing the available area for power net
Why Power Analysis Is Important?
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• With IR drop analysis you see– Voltage levels across the board
– Current density
– Via current and hotspot
– Power loss
DC analysis
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• Heating due to current changes resistance of copper
• Without Thermal effect IR drop estimates will be inaccurate.
• High temperature due to localized current density can cause smoke or fire hazard
• Cadence DC analysis includes effects of – Component heating (power dissipation), including heatsinks
– Joule heating (PCB copper)
What about Thermal effects ?
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• Switching circuit requires current to charge the load.VRM needs to supply this power
• VRM is unable to respond if output impedance exceeds target impedance.– Introduces switching noise:
• Impedance should be smaller than Zt at broad frequency range to lower switching noise.
• AC analysis calculates PDN impedance
Why AC power analysis?
Zt =Vdd * ripple
50% * Imax
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• Add decoupling capacitors, bulk/ceramic capacitors
• Loop inductance’ reduction, effect at higher frequencies– Different decoupling capacitors
– Thinner dielectric
– Location of capacitors
– Change fanout
How to lower impedance?
Low Loop
Inductance
High Loop
Inductance
Low Loop
Inductance
– AC analysis will locate impedance hotspots and helps to get correct capacitor locations
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• To determine proper metal thickness for power/gnd planes
• To find out – If and where to add additional via or power/gnd shape to ease the
overheat
– Whether to add additional plane layers needed in the board stackup
– Power dissipation and temperature profiles in PKG/PCB
– If and where to add sense line compensation for VRM
• Decoupling capacitors – Quantity, type and location
Design Decisions depending on PDN Analysis
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Prodrive Technologies
Bram Bruekers
Since 2003 working at Prodrive Technologies
Analogue / Mixed signal hardware design
PCB design
– 15+ years experience– High current & voltage– Low noise
PCB tooling support & maintenance
11 © 2017 Cadence Design Systems, Inc.
Prodrive Technologies
• One of the fastest growing privately owned technology companies in Europe
• HQ located in Son, Netherlands
• International located: Germany, USA, Israel, China
• Design of electronics, software and mechanics
• Manufacturing• Core competences
– High end computing
– Power conversion
– Motion & mechatronics
– Industrial automation
– Vision & sensing
– IoT
• Industries of main interest:– Industrial
– Automotive
– Infra & energy
– Medical
12 © 2017 Cadence Design Systems, Inc.
MRI Gradient Amplifier
• 3-axes gradient amplifier cabinet
• 2100V / ±1200A Patented end stage
• Maximum 45kW continuous output power for three axes
• Integrated high precision current sensors
• High reliability of >30,000 hours
• Lifetime: >10 years
• Multiple FRUs (Field Replaceable Units)
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Mains Input Board
• Inrush current limiter
• Power distribution
• Integrated current measurements
• Designed for 3x 130A continuous
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Design Choices
• What type of interconnection to use?
Pro Con
Cable Easy / flexible routing Assembly issues, many connections
Where to place electronic circuits?
Bus-bar current carrying capability Difficult to ‘route’ through complex
product
Where to place electronic circuits?
PCB Electronic circuits possible
Ease of assembly
Complex design
Heating
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Design Choices
PCB
• Design complexity
– How many layers ?
– Copper weight ?
– Total Thickness -> Limited by components !
• Thick copper
– Lower temperature ?Not necessarily !
– Higher costs + leadtime PCB FAB house
– PCB Assembly issues
So, thicker is not always better
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Simulation to make design choices
• PCB heating most critical factor for this circuit– Absolute voltage drop not interesting
• Initial stackup : 6 layers 4oz (~140µm) copper – Creating hotspots due to stackup, routing and plane cuts.
– Long leadtime for raw material
– UL certification for 140µm+ copper in several PCB FABs not available
• Final stackup : 12x 2oz (~70µm) copper– Hotspots are more spread because of overlapping planes
– ‘Standard’ available materials = short lead time !
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Comparison 2 PCB stack-ups
Initial Final design
# Layers 6 12
Copper weight 4oz 2oz
Material availability - +++
PCB costs €€€€€ €€€
# PCB Fabs - +++
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Simulated vs. Measured
ΔT simulated ~19˚C ΔT measured ~16˚C
Total current of 390A
No airflow
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Other practical applications
• Feasibility check
• Debugging
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Feasibility
• Question from a customer:
“Can the routing cope with a current of 7A?”
• Microcontroller board– Dense design, not much place for wide traces
• Used PowerDC to simulate the current through the specific part of the PCB– Result: Yes, routing can handle the specified current.
Hotspot is caused by the connector.
Top Bottom
ΔT simulated ~14˚C
Current density
22 © 2017 Cadence Design Systems, Inc.
Debugging
• Issue with core supply of microcontroller– Stability issues during qualification
• IR drop simulation to simulate the voltage drop from the supply to the microcontroller
• Last minute PCB change, extra VIAs were added
• ΔV is about 65mV only ~5mV supply voltage margin!
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Why we use PowerDC
• Initially usage:
– High-current designs IPC2221B / IPC2152 not possible to use on complex boards
– Temperature rise of a PCB
• Now also for power distribution and voltage drop simulations
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• Direct integration with OrCAD/Cadence PCB Editor– Use PI constraints during layout
– DRC markers
• Capable to analyze designs from:– Altium
– Mentor Graphics
– ODB++
– Zuken
Integration with PCB tools
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Automatic Report generation
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For more information visit at booth 4
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For more information visit at booth 6
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For more information:
Visit us at booth 4
www.cb-distribution.nl
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• Cadence PowerDC (DC Analyse, Thermal aware)– Pre- and postlayout
– Setup Layout Constraints
• Cadence Power SI (AC Analysis)– Impedance analysis
– Location and type of capacitors
• Cadence Optimize PI– Automatic decap optimization
– Tradeof between performance, cost
Cadence Power Integrity tools
